August 2020:

General Weather Discussions and Analysis
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DoctorMu
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Cpv17 wrote: Sat Aug 22, 2020 2:25 pm
djmike wrote: Sat Aug 22, 2020 2:21 pm Why such a significant shift east? Wouldnt they have seen that at the 10am? Im seeing many local mets confirming on Fb that the storm is now going to East Louisiana. Thats going to be a major shift for nhc and I know they hate doing that. One local met said it hits central Louisiana then makes a hard left into SETX weakened of course. Ensembles still show Texas. I dont know what to believe anymore. I guess thats why they get paid the big bucks.
The reason for the shift east is because Marco strengthened more than they thought it would. A stronger storm will go more poleward (north) and a weaker system would go more west. The models/track could still change again though because Marco is about to go into the shredder with some high shear which should weaken it but who knows. We’ll see.
Marco is getting sheared now.
Kingwood36
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DoctorMu wrote: Sat Aug 22, 2020 3:54 pm
Cpv17 wrote: Sat Aug 22, 2020 2:25 pm
djmike wrote: Sat Aug 22, 2020 2:21 pm Why such a significant shift east? Wouldnt they have seen that at the 10am? Im seeing many local mets confirming on Fb that the storm is now going to East Louisiana. Thats going to be a major shift for nhc and I know they hate doing that. One local met said it hits central Louisiana then makes a hard left into SETX weakened of course. Ensembles still show Texas. I dont know what to believe anymore. I guess thats why they get paid the big bucks.
The reason for the shift east is because Marco strengthened more than they thought it would. A stronger storm will go more poleward (north) and a weaker system would go more west. The models/track could still change again though because Marco is about to go into the shredder with some high shear which should weaken it but who knows. We’ll see.
Marco is getting sheared now.
What effects will it have if any?
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Ptarmigan
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I see a complex forecast subject to change.
Kingwood36
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I bet they shift east at 4 then shift back west at 10...seems to be the pattern lately
Cromagnum
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Liquid gold. Finally.

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don
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Tropical Storm Marco Discussion Number 10
NWS National Hurricane Center Miami FL AL142020
400 PM CDT Sat Aug 22 2020

Cutting to the chase, there have been some big changes among the
model guidance, and subsequently the NHC forecast, for Marco this
afternoon. While at this point it's a little speculative, the data
collected by this morning's NOAA G-IV flight in the environment
around Marco and across the Gulf of Mexico may have played a key
role in the significant eastward shift seen in nearly all the 12z
models. This isn't to say that the uncertainty in the eventual
track has diminished. In fact, various ensemble members from some
of the global models still show a potential risk to the coast
anywhere from Texas to Alabama, and it's entirely possible that the
volatile shifts seen in the models could continue. That being
said, the new NHC track forecast has been shifted significantly
eastward and now shows the center of Marco reaching southeastern
Louisiana in about 2 days, which is the scenario currently shown by
the GFS, ECMWF, HCCA, Florida State Superensemble, and the TVCN
multi-model consensus. After Marco reaches the coast, the western
Atlantic ridge is expected to build westward and should cause the
cyclone to move more slowly toward the west-northwest across
southern portions of Louisiana.

As far as the intensity is concerned, the last fix made by this
morning's reconnaissance flight indicated that the pressure had
leveled off, and no higher winds had been observed from what was
measured earlier in the flight. The radar presentation from Cuban
radar has also degraded a bit, so Marco's initial intensity is held
at 55 kt. Marco is beginning to move into a zone of moderate
southwesterly shear, but otherwise favorable conditions of warm
ocean water and some upper-level divergence are expected to foster
strengthening during the next day or so. With the exception of the
HWRF, the other intensity models show Marco reaching hurricane
strength, and the NHC foreast continues to show that possibility
while Marco moves over the central Gulf. The shear is still
expected to strengthen in 36-48 hours when the system is approaching
the northern Gulf Coast, but with the shift in the forecast track,
now there may not be enough time for Marco to weaken below
hurricane intensity before it reaches land. The new NHC intensity
forecast is near or just above the HCCA and Florida State
Superensemble models and holds Marco as a hurricane until it reaches
the coast.

The forecast track changes now bring tropical storm force winds to
the coast in 36-48 hours, which necessitates the issuance of
Hurricane and Storm Surge Watches for a portion of the northern
Gulf Coast. These watches will likely need to be upgraded to
warnings later tonight.

Key Messages:

1. Tropical storm conditions will continue over portions of extreme
western Cuba through this evening. Heavy rainfall is also expected
in the eastern portions of the Mexican states of Quintana Roo and
Yucatan, and across far western Cuba, which could result in flash
flooding.

2. Marco is expected to approach the central Gulf Coast as a
hurricane on Monday. Hurricane conditions, life-threatening storm
surge, and heavy rainfall are possible along portions of the Gulf
Coast beginning on Monday, and Hurricane and Storm Surge watches
have been issued. Interests in these areas should follow any advice
given by local government officials.

3. Tropical Storm Laura could bring additional storm surge,
rainfall, and wind impacts to portions of the U.S. Gulf Coast by
the middle of next week. This could result in a prolonged period of
hazardous weather for areas that could be affected by Marco.
Interests there should monitor the progress of Marco and Laura and
updates to the forecast during the next few days.

FORECAST POSITIONS AND MAX WINDS

INIT 22/2100Z 21.9N 85.7W 55 KT 65 MPH
12H 23/0600Z 23.3N 86.5W 65 KT 75 MPH
24H 23/1800Z 25.3N 87.3W 75 KT 85 MPH
36H 24/0600Z 27.5N 88.3W 75 KT 85 MPH
48H 24/1800Z 29.3N 89.6W 65 KT 75 MPH...ON THE COAST
60H 25/0600Z 30.4N 91.1W 50 KT 60 MPH...INLAND
72H 25/1800Z 31.1N 92.7W 40 KT 45 MPH...INLAND
96H 26/1800Z 32.3N 95.6W 25 KT 30 MPH...INLAND
120H 27/1800Z...DISSIPATED

$$
Forecaster Berg
davidiowx
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Pretty big shift for Marco. Looks like we are out of the woods for that one.. for now..
Kingwood36
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Screw it im throwing a big *** bbq on monday...everyone is invited!
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jasons2k
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Wow. I haven’t seen a shift like that in a very long time. Any bets after all this, we don’t get a drop of rain from either system?
davidiowx
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jasons2k wrote: Sat Aug 22, 2020 4:18 pm Wow. I haven’t seen a shift like that in a very long time. Any bets after all this, we don’t get a drop of rain from either system?
Lol right! After seeing what has progressed today, as of right now, I’d bet we won’t get much. But still a lot can change!
Andrew
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jasons2k wrote: Sat Aug 22, 2020 4:18 pm Wow. I haven’t seen a shift like that in a very long time. Any bets after all this, we don’t get a drop of rain from either system?
If it means not getting a hurricane I am fine with that. :D
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Rip76
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jasons2k wrote: Sat Aug 22, 2020 4:18 pm Wow. I haven’t seen a shift like that in a very long time. Any bets after all this, we don’t get a drop of rain from either system?
No way I’m taking that bet.
Cromagnum
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If this pans out, fire up the sprinklers and crank up the AC.

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snowman65
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Are we close enough to landfall that we can start believing that these are at least pretty close maps?
davidiowx
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snowman65 wrote: Sat Aug 22, 2020 4:24 pm Are we close enough to landfall that we can start believing that these are at least pretty close maps?
Not at all. I think Marco is going in to LA. Laura on the other hand, anyone’s guess. Ike came through around the same area as Laura is and at first it was into Florida panhandle, then it shifted all the way to Mexico, then shifted to Galveston. A lot of watching with Laura for sure.
Kingwood36
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I'm ready to track cold fronts and sleet chances ....
Andrew
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snowman65 wrote: Sat Aug 22, 2020 4:24 pm Are we close enough to landfall that we can start believing that these are at least pretty close maps?
The reason the NHC and a lot of others are "more confident" is because upper-level sampling and recon data was ingested into the models for the 12z suite of models. In the past, models usually become more consistent on landfall after data like that is ingested. With that said, I would like to see what the overnight runs show first.
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Stormlover2020
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Icon upper texas coast cat 2 for Laura, showed Marco last night central la
cperk
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The 18Z icon shifted west to the Texas/La border for Laura.
Scott747
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18z GFS obliterates Marco on approach to Louisiana and moves what's left to the w.
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